Filler layer for solar cell module and solar cell module using same

ABSTRACT

The invention mainly aims to provide an economical filler layer for a solar cell module which is excellent in the adhesion property to a transparent front substrate and a backside protective sheet, does not worsen the working environments, and causes no adverse effect on a solar cell element or electrodes at the time of production. To accomplish the aim, the invention provides a filler layer for a solar cell module containing a silane-modified resin obtained by polymerizing an ethylenic unsaturated silane compound and a polyethylene for polymerization and characterized in that the filler layer for a solar cell module has a gel fraction of 30% or lower when the filler layer for a solar cell module is used in a solar cell module.

TECHNICAL FIELD

The invention relates to a filler layer for a solar cell module having asilane-modified resin and a solar cell module using the filler layer.

BACKGROUND ART

In recent years, attention has been paid to a solar cell as a cleanenergy source in light of an upsurge of consciousness of environmentalproblems. At present, solar cell modules in various forms have beendeveloped and suggested.

Generally the solar cell module is produced by laminating a transparentfront substrate, a filler layer, a solar cell element as a photovoltaicdevice, a filler layer, a backside protective sheet, and the like inthis order and then thermally pressure-bonding them by vacuum suction insuch as a lamination method.

Today, as material for composing the filler layer for a solar cellmodule, ethylene-vinyl acetate copolymer resin with a thickness of 100μm to 1500 μm has most commonly been used in terms of theprocessibility, layering workability, production cost, and so forth.

However, the filler layer of the ethylene-vinyl acetate copolymer resinis not necessarily sufficient in the adhesion strength to thetransparent front substrate or the backside protective sheet and has aproblem that the disadvantageous weakness becomes apparent in the longtime use in outdoors. Further, in the case of producing a solar cellmodule using the filler layer of the ethylene-vinyl acetate copolymerresin, the ethylene-vinyl acetate copolymer resin is thermallydecomposed and evolves acetic acid gas and the like depending on theconditions of the thermal pressure bonding. These gases not only worsenthe working environments but also cause adverse effects on the solarcell element and electrodes to result in deterioration and decrease ofelectric power generation efficiency.

Therefore, a method of polymerizing a silane compound with the resin isemployed as a method for providing the resin, which is a material forthe filler layer, with an adhesive property to glass or metals to beused for the transparent front substrate or the backside protectivesheet.

Generally, there are two polymerization methods; a copolymerizationmethod and a graft polymerization method. The copolymerization method isa method carried out by mixing monomers, a catalyst, and an unsaturatedsilane compound and carrying out polymerization reaction at prescribedtemperature and pressure. The graft polymerization method is a methodcarried out by mixing polymers, a free-radical initiator, and anunsaturated silane compound and polymerizing the silane compound to thepolymer main chain or side chains in stirring condition at a prescribedtemperature.

For example, in order to provide strength, heat resistance anddurability to the material itself by causing crosslinking reaction inthe resin, which is the material of the filler layer, at the time ofthermal pressure bonding, the following methods have been proposed; amethod using a resin sheet obtained by adding a silane coupling agentand an organic peroxide to the ethylene-vinyl acetate copolymer resin(Japanese Patent Publication (JP-B; KOKOKU) No. 14111/1987 (i.e., SHO62-14111)); a method using a resin sheet obtained by adding an organicperoxide to an ethylene-vinyl acetate copolymer resin graft-modifiedwith an organic silane compound (Japanese Patent Publication (JP-B;KOKOKU) No. 9232/1987 (i.e., SHO 62-9232)); and a method using a resinsheet obtained by adding an organic peroxide to a ternary copolymerresin of ethylene-ethylenic unsaturated carboxylic acid ester-ethylenicunsaturated silane compound (Japanese Patent Publication (JP-B; KOKOKU)No. 104729/1994 (i.e., Hei 6-104729)), however since these methods alluse the organic peroxide, the organic peroxide is decomposed at the timeof sheet formation to induce crosslinking reaction of the resins to makesheet formation difficult or to deteriorate processibility at the timeof lamination or the decomposition products derived from the organicperoxide remain in the adhesion interfaces and cause adhesion inhibitionat the time of lamination.

There is another problem that the silane compound is expensive andfurther improvements are still required.

DISCLOSURE OF THE INVENTION

Therefore, the invention mainly aims to provide an economical fillerlayer for a solar cell module which is excellent in the adhesionproperty to a transparent front substrate and a backside protectivesheet, does not worsen the working environments, and causes no adverseeffect on a solar cell element or electrodes at the time of production.

To accomplish the aim, the invention provides a filler layer for a solarcell module containing a silane-modified resin obtained by polymerizingan ethylenic unsaturated silane compound and a polyethylene forpolymerization and characterized in that the filler layer for a solarcell module has a gel fraction of 30% or lower when the filler layer fora solar cell module is used in a solar cell module.

Since the above-mentioned filler layer for a solar cell module containsa silane-modified resin, the layer is excellent in the adhesion propertyto a transparent front substrate and a backside protective sheet, e.g.glass, and since the main chain of the resin is a polyethylene, noharmful gas is evolved and the work environments are not worsened.Further, when the filler layer is used for a solar cell module,adjustment of the gel fraction in the filler layer for a solar cellmodule in the above-mentioned range makes it possible to carry outsealing within a short time and makes further heating treatmentunnecessary. Also owing to a low gel fraction as described, the fillerlayer can easily be softened and melted by heating and accordingly,recycling of the solar cell element and the transparent front substrateused for the solar cell module is made possible.

In the present invention, the filler layer for a solar cell modulepreferably further containing a polyethylene. Since the above-mentionedsilane-modified resin is costly, it is preferable for the filler layerfor a solar cell module to contain a polyethylene for addition.

According to the present invention, the polyethylene for polymerizationand the polyethylene for addition are preferably at least onepolyethylene selected from a group of a low density polyethylene, amedium density polyethylene, a high density polyethylene, a very lowdensity polyethylene, an ultra low density polyethylene, and a linearlow density polyethylene.

Moreover, the amount of the silane-modified resin contained in thefiller layer for a solar cell module is preferably in a range of 1 to80% by weight. The above silane-modified resin contains the ethylenicunsaturated silane compound polymerized with the polyethylene forpolymerization, so that the resin is provided with the adhesion propertyto glass or the like. Accordingly, since the filler layer for a solarcell module contains the above-mentioned silane-modified resin, thelayer is provided with a high adhesion property to the transparent frontsubstrate, the backside protective sheet, and the solar cell element.Consequently, if the amount is less than the above-mentioned range, theadhesion property to glass or the like becomes insufficient, and if itexceeds the above-mentioned range, the cost is increased with nopreferable change of the adhesion property to glass or the like.

Further, the filler layer for a solar cell module preferably contains Si(silicon) in a form of a polymerized Si at the amount of 8 ppm to 3500ppm. Similarly to the above-mentioned reasons, it is because controllingof the polymerized Si to be in the range gives good adhesion property tothe solar cell element and the transparent front substrate.

In the present invention, the filler layer for a solar cell modulepreferably contains practically no silanol condensation catalyst. It isbecause this invention is characterized in that the gel fraction in thefiller layer is at a prescribed value or lower. The desired gel fractioncan not be obtained if a silanol condensation catalyst commonly used forwater crosslinking or the like is added to the resin compositioncontaining the ethylenic unsaturated silane compound.

Furthermore, the present invention provides a solar cell modulecomprising the above-mentioned filler layer for a solar cell module. Thesolar cell module having the filler layer for a solar cell module of theinvention is provided with the above-mentioned advantageous points ofthe filler layer e of the invention and is also advantageous in terms ofthe cost.

The filler layer for a solar cell module is excellent in the adhesionproperty to glass to be used for the protection sheet for a solar cellmodule and it does not worsen the working environments. Further, thefiller layer makes it possible to carry out sealing within a short timeat the time of producing the solar cell module and also makes heatingtreatment unnecessary. Moreover, recycling of members contained in thesolar cell module is made possible.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic cross-sectional view showing one example of asolar cell module of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention provides a filler layer for a solar cell module and asolar cell module using the same. Hereinafter, the filler layer for asolar cell module and the solar cell module using the layer will bedescribed. In this connection, a sheet means both of a sheet-likearticle and a film-like article and a film also means both of afilm-like article and a sheet-like article.

A. Filler Layer for a Solar Cell Module

First, the filler layer for a solar cell module of the invention will bedescribed. The filler layer for a solar cell module contains asilane-modified resin obtained by polymerizing an ethylenic unsaturatedsilane compound and polyethylene for polymerization. The filler layer ischaracterized in that the gel fraction is a prescribed value or lowerwhen the filler layer for a solar cell module is used for the solar cellmodule.

Hereinafter, the respective components of the filler layer for a solarcell module will be described.

1. Silane-Modified Resin Composition

The silane-modified resin to be used in the invention is a polymerformed by polymerization of an ethylenic unsaturated silane compound andpolyethylene for polymerization. Such a silane-modified resin isproduced by mixing the ethylenic unsaturated silane compound,polyethylene for polymerization, and a radical initiator, stirring andmelting them at a high temperature, and graft polymerizing the ethylenicunsaturated silane compound with the polyethylene for polymerization.

The polyethylene for polymerization to be used in the invention is notparticularly limited if it is a polyethylene type polymer. Specifically,a low density polyethylene, a medium density polyethylene, a highdensity polyethylene, a very low density polyethylene, an ultra lowdensity polyethylene, or a linear low density polyethylene ispreferable. One or more of them may be used in combination.

Further, as the polyethylene for polymerization is preferably apolyethylene having many side chains. In this connection, polyethyleneshaving more side chains have a low density and polyethylenes having lessside chains have a high density. Accordingly, polyethylenes with a lowdensity are more preferable. The density of the polyethylene forpolymerization in the invention is preferably in a range of 0.850 to0.960 g/cm³ and more preferably in a range of 0.865 to 0.930 g/cm³. Itis because if the polyethylene for polymerization is a polyethylenehaving many side chains, that is, a low density polyethylene, theethylenic unsaturated silane compound is easily graft-polymerized withthe polyethylene for polymerization.

On the other hand, as for the ethylenic unsaturated silane compound usedin the present invention, it is not particularly limited as long as itgraft-polymerized with the polyethylene for polymerization. For example,one or more out of the following can be used: vinyltrimethoxysilane,vinyltriethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane,vinyltributoxysilane, vinyltripentyloxysilane, vinyltriphenoxysilane,vinyltribenzyloxysilane, vinyltrimethylenedioxysilane,vinyltriethylenedioxysilane, vinypropionyloxysilane,vinyltriacetoxysilane, or vinyltricarboxysilane. Vinyltrimethoxysilaneis preferably used in the present invention.

In the invention, the amount of the ethylenic unsaturated silanecompound in the filler layer for a solar cell module is preferably 10ppm or more and further preferably 20 ppm or more. The filler layer fora solar cell module contains the ethylenic unsaturated silane compoundpolymerized with the polyethylene for polymerization, so that the goodadhesion property to a material, e.g. glass, to be employed for thetransparent front substrate and the rear sheet for a solar cell module,which will be described later, can be provided. Accordingly, if theamount is less than the above range, the adhesion property to glassbecomes insufficient. An upper limit of the amount of the ethylenicunsaturated silane compound is preferably 4000 ppm or less and furtherpreferably 3000 ppm or less. The upper limit is not limited in terms ofthe adhesion property to glass or the like, if it exceeds theabove-mentioned range, the cost is increased although the adhesionproperty to glass is not changed.

It is preferable for the above-mentioned silane-modified resin to becontained in a range of 1 to 80% by weight in the above-mentioned fillerlayer for a solar cell module and it is more preferable in a range of 5to 70% by weight. Also in this case, similarly as described, thesilane-modified resin is provided with a adhesion property to glass orthe like by existence of the ethylenic unsaturated silane compoundpolymerized with the polyethylene for polymerization. Accordingly, thefiller layer for a solar cell module has a high adhesion property toglass since it contains the silane-modified resin as described above.Consequently, in terms of the adhesion property to glass or the like andthe cost, the silane-modified resin is used preferably in theabove-mentioned range.

The silane-modified resin has a melt mass flow rate at 190° C.preferably in a range of 0.5 to 10 g/10 minute and more preferably in arange of 1 to 8 g/10 minute. It is because the formability of the fillerlayer for a solar cell module and the adhesion property and the like tothe transparent front substrate and the backside protective sheet aremade excellent.

The melting point of the silane-modified resin is preferably 110° C. orlower. At the time of producing a solar cell module using the fillerlayer for a solar cell module, the above-mentioned range is preferablein terms of the processibility or the like.

Examples of a radical generation agent to be added to thesilane-modified resin are organic peroxides, e.g. hydroperoxides such asdiisopropylbenzene hydroxyperoxide and2,5-dimethyl-2,5-di(hydroperoxy)hexane; dialkylperoxides such asdi-tert-butyl peroxide, tert-butylcumyl peroxide, dicumyl peroxide,2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and2,5-dimethyl-2,5-di(tert-peroxy)hexyn-3; diacyl peroxides such asbis(3,5,5-trimethylhexanoyl)peroxide, octanoyl peroxide, benzoylperoxide, o-methylbenzoyl peroxide, and 2,4-dichlorobenzoyl peroxide;peroxy esters such as tert-butylperoxy acetate,tert-butylperoxy-2-ethylhexanoate, tert-butylperoxy pyvalate,tert-butylperoxy octoate, tert-butylperoxyisopropyl carbonate,tert-butylperoxybenzoate, di-tert-butylperoxy phthalate,2,5-dimethyl-2,5-di(benzoylperoxy)hexane, and2,5-dimethyl-2,5-di(benzoylperoxy)hexyn-3; and ketone peroxides such asmethyl ethyl ketone peroxide and cyclohexanone peroxide; and azocompounds such as azobis(isobutyronitrile) andazobis(2,4-dimethylvaleronitrile).

The used amount of the radical initiator is preferable to be added in anamount of 0.001% by weight or more in the silane-modified resin. This isbecause if it is less than the above-mentioned range, the radicalpolymerization of the ethylenic unsaturated silane compound and thepolyethylene for polymerization is difficult to be caused.

The silane-modified resin to be used in the invention may be used forlaminate glass. The laminate glass is produced by sandwiching a soft andtough resin or the like between glass plates and thermally pressurebonding the plates. Therefore, in terms of the adhesion property toglass, the above-mentioned silane-modified resin can be used.

2. Polyethylene for Addition

In the invention, the filler layer for a solar cell module is preferableto contain the above-mentioned silane-modified resin and a polyethylenefor addition. Examples of the polyethylene for addition are thosesimilar to the polyethylenes exemplified in the paragraph “1.Silane-modified resin”. In the invention, the polyethylene for additionis particularly preferable to be the same as the above-mentionedpolyethylene for polymerization. It is because since the silane-modifiedresin is costly, rather than the formation of the filler layer for asolar cell module using the silane-modified resin alone, formation ofthe filler layer for a solar cell module by adding the polyethylene foraddition with the silane-modified resin is advantageous in terms of thecost.

The content of the polyethylene for addition is preferably 0.01 part byweight to 9,900 parts by weight and more preferably 90 parts by weightto 9,900 parts by weight to the silane-modified resin 100 parts byweight.

When two or more kinds of the silane-modified resins are used, thecontent of the polyethylene for addition is preferable to be in theabove-mentioned range to the resins 100 parts by weight in total.

The polyethylene for addition is preferable to have a melt mass flowrate at 190° C. in a range of 0.5 to 10 g/10 minute and more preferableto have it in a range of 1 to 8 g/10 minute. It is because theformability or the like of the filler layer for a solar cell modulebecomes excellent.

The melting point of the polyethylene for addition is preferable to be130° C. or lower. This range is preferable in terms of theprocessibility or the like at the time of producing the solar cellmodule using the filler layer for a solar cell module.

A melting point measurement method is carried out by differentialscanning calorimetry (DSC) according to the measurement method oftransition temperature of plastics (JISK 7121). In this connection, whentwo or more melting points exist, the higher temperature is defined tobe the melting point.

3. Additives

In the invention, as needed, additives such as a light stabilizer, anultraviolet absorbent, a thermal stabilizer, or the like may be used. Ifthe filler layer for a solar cell module of the invention contains theabove-mentioned silane-modified resin and additionally contains a lightstabilizer, an ultraviolet absorbent, a thermal stabilizer, or the like,the mechanical strength, adhesion strength, prevention of yellowing,prevention of cracking, and excellent suitability for processing can beprovided.

The light stabilizer is an agent for catching active species whichinitiate photo-deterioration in the polymers to be used for thepolyethylene for polymerization and the polyethylene for addition andaccordingly preventing photooxidation. Specifically, at least one kindof compounds selected from hindered amine type compounds, hinderedpiperidine type compounds, and others can be used.

The ultraviolet absorbent is an agent for absorbing harmful ultravioletrays in the sun light and converting the ultraviolet rays into harmlessheat energy in the molecules and accordingly preventing excitation ofthe active species which initiate photo-deterioration in the polymers tobe used for the polyethylene for polymerization and the polyethylene foraddition. Specifically, at least one kind of inorganic type ultravioletabsorbents selected from a group of consisting of benzophenone type,benzotriazole type, salicylate type, acrylonitrile type, metal complexsalt type, hindered amine type ultraviolet absorbents, ultra fineparticles of titanium oxide (particle diameter: 0.01 μm to 0.06 μm), andultra fine particles of zinc oxide (particle diameter: 0.01 μm to 0.04μm) can be used.

Examples of the thermal stabilizer may include phosphorus type thermalstabilizers such as tris(2,4-di-tert-butylphenyl)phosphite,bis[2,4-bis(1,1-dimethylethyl)-6-methylphenyl]ethyl ester phosphite,tetrakis(2,4-di-tert-butylphenyl)[1,1-biphenyl]-4,4′-diylbisphosphonite, and bis(2,4-di-tert-butylphenyl)pentaerythritoldisphosphite; and lactone type thermal stabilizers such as a reactionproduct of 8-hydroxy-5,7-di-tert-butyl-furan-2-one and o-xylene. One ormore of them maybe used in combination. Among them, a phosphorus typethermal stabilizer and a lactone type thermal stabilizer may be used incombination.

The content of the light stabilizer, the ultraviolet absorbent, and thethermal stabilizer is preferably in a range of 0.01 to 5% by weight inthe filler layer for a solar cell module, although it differs dependingon the particle shape, the density and the like.

In the case of being used for a solar cell module, the filler layer fora solar cell module is characterized in that the gel fraction is low asit is described later and therefore, it is unnecessary to form acrosslinked structure of the silane-modified resin. Accordingly, acatalyst or the like for promoting condensation reaction of acrosslinking agent or silanol groups is not particularly needed.

Specifically, it is preferable that a silanol condensation catalyst e.g.dibutyl tin diacetate, dibutyl tin dilaurate, dibutyl tin dioctanoate,and dioctyl tin dilaurate, for promoting dehydration condensationreaction of silanol groups in silicone, is not practically contained.Here, the catalyst is not practically contained means the case that thecontent is 0.05 part by weight or less in the resin compositioncomposing the filler layer for a solar cell module 100 parts by weight.

4. Filler Layer for a Solar Cell Module

The thickness of the filler layer for a solar cell module of theinvention is preferably in a range of 10 to 2000 μm and especiallypreferably in a range of 100 to 1250 μm. In the case the thickness isthinner than the above-mentioned range, the layer cannot support a cellto result in easiness of breakage of the cell. When the thickness isthicker than the above-mentioned range, the weight of the module becomesheavy while also worsen the workability at the time of installation, andthe cost performance is also disadvantageous.

In the invention, it is preferable that Si (silicon) is contained at aratio by weight in a range of 8 ppm to 3500 ppm, more preferably in arange of 10 ppm to 3000 ppm, and even more preferably in a range of 50ppm to 2000 ppm in the filler layer for a solar cell module. It isbecause when Si is contained in form of polymerized Si at a ration byweight in the above-mentioned range, the adhesion property to thetransparent front substrate and the solar cell element can be kept good.Also the above-mentioned range is preferable in term of the cost.

As a method of measuring the weight ratio of the polymerized Si may beemployed a method involving steps of burning only the filler layer to beash by heating and thereby converting the polymerized Si into SiO₂,melting the ash in an alkali, dissolving the resulting ash in purewater, adjusting the volume to be constant, and carrying out ICP opticalemission spectrometry (high frequency plasma emission spectrometer ICPS8100, manufactured by Shimadzu Corporation).

As the resin composing the filler layer for a solar cell module, thosewhich have the melt mass flow rate at 190° C. in a range of 0.5 to 10g/10 minute are preferable and those having it in a range of 1 to 8 g/10minute are more preferable. It is because the formability of the fillerlayer for a solar cell module, the adhesion property to the transparentfront substrate and the backside protective sheet and other factros aremade excellent.

The melting point of the resin composing the filler layer for a solarcell module is preferably 130° C. or lower. The above-mentioned range ispreferable in terms of the processibility at the time of producing thesolar cell module using the filler layer for a solar cell module. Thisis also because if the melting point is about the above-mentionedtemperature, recycling of parts composing the solar cell module, e.g.solar cell element and the transparent front substrate is made easy whenthey are re-utilized. The measurement method of the melting point is thesame as described above and therefore no further explanation isdescribed here.

In the case the filler layer for a solar cell module of the invention isused for the solar cell module, the gel fraction is preferably 30% orlower, more preferably 10% or lower, and even more preferably 0%. Sincethe silane-modified resin to be used in the invention does not form acrosslinked structure as described, sealing can be carried out within ashort time and post-treatment such as heating treatment is unnecessary.Also, if the gel fraction exceeds the above-mentioned range, theprocessibility at the time of production of the solar cell module isdeteriorated and no improvement of the adhesion property to thetransparent front substrate and the backside protective sheet isobserved. Further, if the gel fraction exceeds the above-mentionedrange, recycling of parts composing the solar cell module, e.g. solarcell element and the transparent front substrate is made difficult.

The gel fraction in the case the filler layer for a solar cell module isused in the solar cell module means the gel fraction of the filler layerfor a solar cell module after the solar cell module is produced by aconventional formation method such as a lamination method involvingsteps of successively laminating a transparent front substrate, a fillerlayer for a solar cell module, a solar cell element, a filler layer fora solar cell module, and a backside protective sheet in this order andthen thermally pressure-bonding the united body by vacuum suction.

As a measurement method of the gel fraction is employed a methodinvolving steps of weighing a sample of the filler layer for a solarcell module 1 g, putting it in a wire-netting bag with 80 meshes,loading the sample together with the bag in a Soxhlet extractor, andrefluxing xylene at the boiling point. After the continuous extractionfor 10 hours, the sample is taken out together with the bag and dried toweigh. The weights before and after extraction are compared to measurethe % by weight of the remaining insoluble matter for using it as thegel fraction.

5. Production Method of Filler Layer for Solar Cell Module

Next, a production method of the filler layer for a solar cell module ofthe invention will be described.

First, a preparation method of the silane-modified resin to be used inthe invention will be described. The silane-modified resin can beobtained by thermally melting and mixing an ethylenic unsaturated silanecompound, a polyethylene for polymerization, and a radical initiator andthereby graft polymerizing the ethylenic unsaturated silane compoundwith the polyethylene for polymerization.

The thermally melting and mixing method of the mixture is notparticularly limited. Regarding an additive, however, it is preferableto employ a method carried out by mixing a master batch, which containsa resin previously mixed and kneaded with the additive, with main rawmaterials and extrusion-melting the mixture. The heating temperature ispreferably 300° C. or lower and more preferably 270° C. or lower. Theabove-mentioned silane-modified resin is easy to be crosslinked andgelled in the silanol group portions by heating, so that the melting andmixing is preferable to be carried out in the above-mentioned range.

Next, a formation method of the filler layer for a solar cell module ofthe invention will be described. As described above, it may be possiblethat after the silane-modified resin is thermally melted and mixed, theobtained silane-modified resin is formed into pellets and againthermally melted and mixed and extruded. It may also be possible tofeeding the silane-modified resin and the polyethylene for addition to ahopper of an extruder and thermally melting the mixture in the cylinder.The latter is excellent in terms of the cost.

After the resin is heated and melted as described above, the melt isformed to be like a sheet with a thickness of 100 to 1500 μm by aconventional method such as a T-die or inflation molding and form thefiller layer for a solar cell module.

The heating temperature at the time of thermally melting again ispreferably 300° C. or lower and more preferably 270° C. or lower. Asdescribed, the silane-modified resin is easy to be crosslinked andgelled in the silanol group portions by heating, so that it ispreferable for the resin to be melted by heating in the above range oftemperature and then extruded.

B. Solar Cell Module

Next, a solar cell module of the invention will be described. The solarcell module of the invention is characterized in that the module has theabove-mentioned filler layer for a solar cell module. FIG. 1 is aschematic cross-sectional view of a solar cell module produced using thefiller layer for a solar cell module. As shown in FIG. 1, the solar cellmodule T is produced by a common formation method such as a laminationmethod carried out by laminating a transparent front substrate 1, afiller layer for a solar cell module 2, a solar cell element 3 as aphotovoltaic device, a filler layer for a solar cell module 2, and abackside protective sheet 4 in this order and then thermallypressure-bonding them to be a united body by vacuum suction.

In the invention, the lamination temperature when such a laminationmethod is employed is preferably in a range of 90° C. to 230° C. andmore preferably in a range of 110° C. to 190° C. If the temperature islower than the above-mentioned range, melting becomes insufficient andthe adhesion property to the transparent front substrate, an auxiliaryelectrode, the solar cell element, the backside protective sheet tends,and the like to be deteriorated. If it is higher than the above range,water crosslinking owing to moisture in the atmospheric air tends to bepromoted and the gel fraction tends to become high, thus, it is notpreferable. The lamination time is preferably in a range of 5 to 60minutes and more preferably in a range of 8 to 40 minutes. If the timeis shorter than the above-mentioned range, melting becomes insufficientand the adhesion property to the members tends to be deteriorated. If itis longer, it becomes a problem in terms of the production process andparticularly in accordance with the temperature ad the humidityconditions and it may possibly result in increase of the gel fraction.With respect to the humidity, if it is too high, the gel fraction isincreased and if it is too low, the adhesion property to various membersmay possibly be decreased, however if it is in a normal humidity levelunder common atmospheric environments, no particular problem is caused.

In the invention, the filler layer for a solar cell module may be formedbetween the transparent front substrate and the solar cell element ormay be formed between the transparent front substrate and the solar cellelement and between the backside protective sheet and the solar cellelement.

Further, in the solar cell module of the invention, other layers mayoptionally be laminated for a purpose of the sun light absorption,reinforcement, and other purposes.

As the transparent front substrate to be employed for the solar cellmodule of the invention, glass, a fluorine resin sheet, and atransparent composite sheet obtained by laminating a weatheringresistant film and a barrier film may be used.

As the backside protective sheet to be employed for the solar cellmodule of the invention, a metal such as aluminum, a fluorine resinsheet, and a composite sheet obtained by laminating a weatheringresistant film and a barrier film may be used.

C. Recycling of Solar Cell Module

As described above, in the invention, since the gel fraction of thefiller layer in the solar cell module is adjusted to be a prescribedrange, members of the used solar cell module and defective solar cellmodules outputted during the production process, more specifically thesolar cell element and the transparent front substrate can bere-utilized. Hereinafter, with respect to the recycling, a productionmethod of a recovered solar cell, a production method of a recycledtransparent front substrate, and a production method of a recoveredsolar cell module will be described separately.

(1) Production Method of Recovered Solar Cell

First, a production method of recovered solar cell will be described.The production method of recovered solar cell is a recovered solar cellproduction method for obtaining a recovered solar cell from theabove-mentioned solar cell module of the invention and involvesprocesses of: heating process wherein the solar cell module is heated ata temperature equal to or higher than the melting point of the resincomposing the filler layer, separation process wherein the solar cellelement is separated from the filler layer plasticized by heating, andremoving process wherein the filler layer adhering to the solar cellelement is removed. Hereinafter, the respective processes will bedescribed.

1. Heating Process

In the heating process, the solar cell module is heated at a temperatureequal to or higher than the melting point of the resin composing thefiller layer. Heating the solar cell module at a temperature equal to orhigher than the melting point of the resin composing the filler layer asdescribed makes it possible to soften and melt the resin composing thefiller layer and accordingly easily remove the filler layer.

The heating method may be a method of feeding the solar cell module ofthe invention into a container filled with a heated gas, liquid, a solidsuch as a powder, or combinations thereof or a method of holding thesolar cell module on a heated hot plate.

Heating temperature is a temperature equal to or higher than the meltingpoint of the resin composing the filler layer and properly selectedaccording to the employed resin. The softening point means Vicatsoftening temperature measured according to JIS K7206 standard of theabove-mentioned thermoplastic resin. The heating temperature in theheating process is equal to the Vicat softening temperature or higherthan that preferably by 0° C. to 250° C., more preferably by 10° C. to150° C., or even more preferably by 20° C. to 130° C.

Specific heating temperature in the heating process is preferably in arange of 20° C. to 450° C., more preferably 30° C. to 350° C., and evenmore preferably 110° C. to 170° C.

2. Separation Process

The separation process in the invention is a process of separating thesolar cell element by utilizing the softening and melting of the fillerlayer by heating in the heating process. The separation process may becarried out by any separation method if it can separate the solar cellelement without damaging the element.

As the separation method, a method of using separation means or a methodof applying shearing stress may be employed.

The method of using separation means is a method of separating thetransparent front substrate and the backside protective sheet from thesolar cell element by passing the cutting means through the filler layerformed between the transparent front substrate and the solar cellelement and the filler layer formed between the solar cell element andthe backside protective sheet of the solar cell module heated in theheating process. Such separation means is not particularly limited if itcan cut the softened filler layer and a wire can be exemplified as apreferable means.

The method of applying shearing stress is a method of separating thetransparent front substrate and the backside protective sheet from thesolar cell element by applying shearing stress to the filler layer whilepushing at least one of the solar cell element and the transparent frontsubstrate or at least one of the solar cell element and the backsideprotective sheet of the solar cell module heated in the heating processin a lateral direction.

3. Removing Process

In the removing process in the invention, the filler layer adhering tothe solar cell element after separation is removed. As the removalmethod, physical washing of physically removing the filler layer,chemical washing of chemically removing the filler layer, or combinationthereof may be exemplified.

The physical washing includes such as a method of blowing a gas, aliquid, a solid, or combinations thereof or a method of wiping with acloth. The physical washing is preferable to be carried out in the statethat the filler layer is heated. For example, an air blast method and ashot blast method of jetting compressed air and steel ball shots at ahigh speed by using compressed air or centrifugation in heatingatmosphere can be exemplified. The physical washing is advantageous whenthe adhering substances are in the portion existing in the filler layer.

In the physical washing, it is required to remove the adhering substancewithout damaging the solar cell element to be re-utilized. Therefore,for instance, when the filler layer is removed by blowing fineparticles, the particle diameter of the fine particles is preferably ina range of 5 μm to 500 μm. As a solid usable for the physical washing, asteel type grinding material, a stainless steel grinding material, azinc grinding material, a copper grinding material, an alumina grindingmaterial, a silicon carbide grinding material, glass grinding material,a resin grinding material, silica sand, ceramic beads, zirconia, slag,calcium carbonate, sodium bicarbonate, and the like may be employed.

As a liquid, a heated organic solvent and a metal liquid may beemployed.

As a gas, an inert gas such as air, nitrogen gas, argon gas, and heliumgas may be employed.

Specifically, a method for removing the separated layer from the solarcell element by immersing the separated solar cell element in an organicsolvent such as xylene and refluxing xylene or other method can beexemplified.

As the chemical washing, an acid or alkali treatment method and a methodfor dissolution in a solvent can be exemplified. The solvent to be usedfor the chemical washing can properly be selected depending on theadhering filler layer.

As the method of combining the physical washing and chemical washing, amethod for completely removing the adhering substance by air blast orshot blast after immersion in a liquid capable of dissolving theadhering substance for a certain period can be exemplified.

The adhering substance can be removed in the above-mentioned manner andif necessary, washing with alcohol or the like is carried out further toeasily produce the recovered solar cell from the used solar cell module.

(2) Production Method of Recovered Transparent Front Substrate

Next, a production method of a recovered transparent front substratewill be described. The production method of the recovered transparentfront substrate is a recovered transparent front substrate productionmethod for obtaining the recovered transparent front substrate from thesolar cell module of the invention above-mentioned and involvesprocesses of: heating process wherein the solar cell module is heated ata temperature equal to or higher than the melting point of the resincomposing the filler layer and having the gel fraction at a prescribedvalue or lower, separation process wherein the filler layer plasticizedby heating is parted in order to separate the recovered transparentfront substrate, and removing process wherein the filler layer adheringto the transparent front substrate is removed. Hereinafter, therespective processes will be described.

1. Heating Process

In the heating process, the transparent front substrate can easily beseparated from the filler layer by heating the solar cell module at atemperature equal to or higher than the softening point of the resincomposing the filler layer. The heating method and the heatingtemperature are the same as described in the paragraph: (1) Productionmethod of recovered solar cell. Thus, no further explanation isdescribed here.

2. Separation Process

In the separation process, the transparent front substrate is parted andseparated from the filler layer softened and melted by heating in theheating process. The separation method is not particularly limitedunless the method damages the transparent front substrate.

Specific examples may include the separating means described in theparagraph: (B) Production method of recovered solar cell, and the methodof applying shearing stress.

3. Removing Process

In the removing process, the filler layer adhering to the transparentfront substrate is removed. The removing method can be carried out byphysical washing, chemical washing or their combination similarly to themethod described in the paragraph:

(1) Production method of recovered solar cell. Details are same asdescribed and therefore no further explanation is described here.

After the removal of the filler layer, if necessary, washing with analcohol or the like is carried out to easily produce a recoveredtransparent front substrate from the used solar cell module.

(3) Recycling Method of Solar Cell Module

Finally, a recycling method of the solar cell module will be described.The recycling method of the solar cell module is a solar cell modulerecycling method for recycling members from the solar cell moduledescribed in the paragraph: B. Solar cell module, and involves processesof: heating process wherein the solar cell module is heated at atemperature equal to or higher than the melting point of the resincomposing the filler layer, separation process wherein the solar cellelement is separated by parting the member from the filler layerplasticized by heating.

The solar cell module recycling method makes it possible to recycle(recycle or reuse) of members such as a solar cell element contained ina solar cell module, which is determined to be a defective product atthe time of solar cell module processing, or members such as a solarcell element contained in a collected used solar cell module. The methodis not only advantageous in terms of the cost but also preferable inconsideration of the global environmental preservation.

The solar cell module to be subjected to the solar cell module recyclingmethod may include, as described above, a solar cell module, which isdetermined to be a defective product at the time of solar cell moduleprocessing and a solar cell module which is used and collected.

In the invention, such solar cell modules are to be subjected to theheating process and separation process. The heating process andseparation process are the same as those described in paragraphs: (1)Production method of recovered solar cell and (2) Production method ofrecovered transparent front substrate. Thus, no further explanation isdescribed here.

In addition, in the recycling method of the solar cell module, it ispreferable to carry out process of separating backside protective sheetsimultaneously in the separation process.

For example, when a material such as a fluorine resin which evolves aharmful gas by heating is used for the backside protective sheet,separation of the backside protective sheet from the solar cell modulein the process of separating backside protective sheet makes it possibleto prevent harmful gas evolution attributed to heating of the backsideprotective sheet at the time of recycling of the solar cell module.Thus, the load on ambient environments can be lessened.

Separation of the backside protective sheet can be carried outsimultaneously with the above-mentioned separation of the solar cellelement or the transparent front substrate or before separation of thesemembers.

The treatment after the separation process differs depending on whetherthe members are used as they are (reuse) or whether the members are usedas materials (recycle). In the case of reuse, if the members are thesolar cell element and the transparent front substrate, they are reusedby the treatment methods described in the paragraphs: (1) Productionmethod of recovered solar cell and (2) Production method of recoveredtransparent front substrate. On the other hand, in the case of recycle,the members are recycled according to the recycling method describedbelow.

Whether members are reused or recycled may be determined on acase-by-case basis: it is determined in the solar cell module state suchas when the solar cell element is apparently broken, and it isdetermined depending on the conditions of the members such as the solarcell element, the transparent front substrate, and the like composingthe solar cell module after separation process.

(Recycle Method)

In the re-utilization method of the solar cell module, recycle methodsof the solar cell element and the transparent front substrate among themembers of the solar cell module will be described.

1. Solar Cell Element

In the case such as when the element is damaged after the separationprocess, the above-mentioned removing process is not carried out orafter the process is carried out, the element is recycled for purposesto be used other than the solar cell element.

Specifically, the element is melted again for recovering a Si ingot orwhen a large quantity of an impurity exists in Si, it is used for otherpurposes.

2. Transparent Front Substrate

Also in this case, after the separation process, no above-mentionedremoving process is carried out or the removing process is carried outand then the transparent front substrate is used for other purposes.Specifically, it is recovered in form of glass raw material (cullet) andmelted and formed into plate glass.

While the invention has been described with reference to specificembodiments, the description is illustrative of the invention and is notto be construed as limiting the invention. It is therefore intended thatthe technical scope of the invention encompass any modifications whichcomprise the construction substantially equal to the technical idea asdefined by the appended claims and have the same effect.

EXAMPLES

Hereinafter, the invention will be described further in detail withreference to examples.

Example 1

(1) Preparation of Silane-modified Resin

A linear low density polyethylene (referred to as LLDPE in Tables)having a density of 0.898 g/cm³ and a melt mass flow rate (referred toas MFR in Tables) at 190° C. of 2 g/10 min 98 parts by weight was mixedwith vinyltrimethoxysilane 2 parts by weight and as a radical initiator,dicumyl peroxide 0.1 part by weight and heated, melted, and stirred at200° C. to obtain a silane-modified resin.

(2) Formation of Filler Layer for Solar Cell Module

The above-mentioned silane-modified resin 5 parts by weight, a linearlow density polyethylene having a density of 0.898 g/cm³ 95 parts byweight, and a separately produced a master batch containing a lightresistant agent, UVA, and an antioxidant (obtained by mixing a hinderedamine type light stabilizer 2.5 parts by weight, a benzophenone typeultraviolet absorbent 7.5 parts by weight, and a phosphorus type thermalstabilizer 5 parts by weight were mixed with a linear low densitypolyethylene 85 parts by weight and the mixture was melted and processedto be pellets) 5 parts by weight were mixed and led to a hopper of afilm forming apparatus having a φ25 mm extruder and a T die with 300 mmwidth and formed into a 400 μm-thick sheet at drawing speed of 3 m/minand 230° C. extrusion temperature. The film formation could be carriedout without any problem. A filler layer for a solar cell module wasobtained through the series of the processes.

(3) Production of Solar Cell Module

Using the filler layer for a solar cell module with a thickness of 400μm produced in (2), a glass plate with a thickness of 3 mm, the fillerlayer for a solar cell module with a thickness of 400 μm, a crystalsilicon solar cell element, the filler layer for a solar cell modulewith a thickness of 400 μm mentioned above, and a laminated sheetcomposed of a 38 μm-thick polyfluorovinyl type resin sheet (PVF), a 30μm-thick aluminum foil, and a 38 μm-thick polyfluorovinyl type resinsheet (PVF) were laminated through acrylic resin type adhesive layersand while the solar cell element was set upward, the laminated body wasthermally pressure-bonded at 150° C. for 15 minutes by a vacuumlaminator for solar cell module production to obtain a solar cellmodule.

Examples 2 to 11

(1) Preparation of Silane-modified Resin

silane-modified resins were produced in the same manner as Example 1with polyethylene for polymerization, the ethylenic silane compounds,and the radical initiators shown in Table 1 at the respective mixingratios.

TABLE 1 polyethylene for polymerization ethylenic MFR unsaturateddensity [g/10 silane radical mixing type [g/cm³] minutes] compoundinitiator ratio Example 1 LLDPE 0.898 3.5 vinyltrimethoxysilane dicumyl98:2:0.10 peroxide Example 2 LLDPE 0.918 4.0 vinyltrimethoxysilanet-butylperoxy- 98:2:0.20 2-ethyl hexanoate Example 3 LLDPE 0.880 2.2vinyltripropoxysilane dicumyl 97:3:0.15 peroxide Example 4 LLDPE 0.90611 vinyltrimethoxysilane dicumyl 98:2:0.15 peroxide Example 5 LLDPE0.935 3.5 vinyltrimethoxysilane dicumyl 97:3:0.15 peroxide Example 6Same as Example 1 Example 7 Same as Example 1 Example 8 Same as Example1 Example 9 Same as Example 1 Example 10 Same as Example 1 Example 11Same as Example 1 Comparative — Example 1 Comparative Same as Example 1Example 2 Comparative Same as Example 1 Example 3 Comparative Same asExample 1 Example 4(2) Formation of Filler Layer for a Solar Cell Module

The filler layers for a solar cell module were obtained in the samemanner as Example 1 in the conditions shown in Table 2. In Table, VLDPErepresents a very low density polyethylene and LDPE represents a lowdensity polyethylene.

TABLE 2 polyethylene for addition mixing ratio MFR silane- polyethyleneextrusion density [g/10 modified for master crosslinking temperaturetype [g/cm³] minutes] resin addition batch agent [° C.] Example 1 LLDPE0.898 3.5 5 95 5 — 230 Example 2 LLDPE 0.918 4.0 2 98 5 — 230 Example 3LLDPE 0.880 2.2 10 90 5 — 230 Example 4 LLDPE 0.906 11 10 90 5 — 230Example 5 LLDPE 0.935 3.5 10 90 5 — 230 Example 6 VLDPE 0.884 1.0 10 905 — 240 Example 7 LDPE 0.917 7.2 20 80 5 — 230 Example 8 LLDPE 0.898 3.540 60 5 — 230 Example 9 LLDPE 0.898 3.5 40 60 5 — 230 Example 10 — 100 05 — 230 Example 11 — 100 0 5 — 230 Comparative LLDPE 0.898 3.5 — 100 5 —230 Example 1 Comparative LLDPE 0.898 3.5 5 100 — — 230 Example 2Comparative LLDPE 0.898 3.5 20 80 5 5 230 Example 3 Comparative — 100 05 5 230 Example 4(3) Production for Solar Cell Module

The solar cell modules were obtained in Examples 2 to 8 in the samemanner as Example 1. The solar cell modules were obtained in Examples 9and 10 in the same manner as Example 1, except that heat pressurebonding was carried out at 170° C. for 15 minutes by the vacuumlaminator. Further, the solar cell module was obtained in Example 11 inthe same manner as Example 1, except that heat pressure bonding wascarried out at 170° C. for 30 minutes.

Comparative Example 1

Production was carried out in the same manner as Example 1, except thatno silane-modified resin was used.

Comparative Example 2

Production was carried out in the same manner as Example 1, except thatno master batch was used.

Comparative Examples 3 and 4

Under conditions shown in Table 2, the solar cell modules were obtainedas in Example 1, except that the filler layers for a solar cell modulewere formed in the same manner as Example 1. A master batch 5 parts byweight which contains dibutyltin dilaurate 1 part by weight was used asthe crosslinking agent and added by mixing with the silane-modifiedresin, LLDPE, a master batch containing the light resistant agent, UVA,and the antioxidant and forming a film in the same manner as Example 1.

[Evaluation]

The filler layers for a solar cell module obtained in Examples 1 to 11and Comparative Examples 1 to 4 were subjected to total lighttransmittance measurement: the glass adhesion property, gel fraction,and filler removal state in the filler layers for a solar cell modulewere observed after solar cell module production: and the electromotiveforce decrease ratio of the solar cell modules was measured in thefollowing conditions. The evaluation results are shown in Table 3.

(Total Light Transmittance)

The total light transmittance was measured for each filler layer for asolar cell module by using a color computer. Specifically, a sheet ofthe filler layer for a solar cell module was sandwiched between a frontand a rear ethylene-tetrafluoroethylene copolymer films (trade name:AFLEX 100 N, manufactured by ASAHI GLASS CO., LTS.) and pressure-bondedat 150° C. for 15 minutes by a vacuum laminator for production of asolar cell module. Then the ethylene-tetrafluoroethylene copolymer filmswere separated and only the heated sheet of the filler layer for a solarcell module was subjected to measurement.

The solar cell module was kept still in high temperature and highhumidity conditions of 85° C. and 85% humidity for 1000 hours. Then theseparation strength from glass, which was the transparent frontsubstrate, and the filler layer for a solar cell module was measured.

(Gel Fraction)

The measurement was carried out by the method described in theparagraph: A. Filler layer for a solar cell module.

(Filler Removal State)

Each solar cell module was produced and then the solar cell element andthe backside protective sheet were separated from the transparent frontsubstrate (a glass plate) by using a wire in a silicone oil heated at180° C. after the module was cooled. Thereafter, the silicone oil wasremoved by washing and the transparent front substrate (the glass plate)bearing remaining filler layer was put on a hot plate kept at 180° C.and the remaining filler layer was wiped out with a cloth. The easinessof the wiping at that time and the remaining state after the wiping wereevaluated.

(Electromotive Force Decrease Ratio)

The environmental test of each solar cell module was carried outaccording to JIS C 8917-1989 standard and output of thephotoelectromotive force was measured before and after the test.

TABLE 3 electro- total motive light force trans- glass gel fillerdecrease mittance adhesion fraction removal ratio [%] property [%] state[%] Example 1 88 good 0 easily <5 removable Example 2 86 good 0 easily<5 removable Example 3 89 good 0 easily <5 removable Example 4 86 good 0easily <5 removable Example 5 85 good 0 easily <5 removable Example 6 85good 0 easily <5 removable Example 7 74 good 0 easily <5 removableExample 8 89 good 0.7 easily <5 removable Example 9 89 good 9.6 easily<5 removable Example 10 88 good 16.1 easily <5 removable Example 11 90good 28.2 easily <5 removable Comparative 88 no 0 easily — Example 1adhesion removable Comparative 88 good 0 easily 10 Example 2 removableComparative 90 good 32 partially <5 Example 3 impossible to removeComparative 91 good 44 no removal <5 Example 4

As sown in Table 3, the filler layers for a solar cell module ofexamples were excellent in the appearance and the total lighttransmittance. With respect to the separation strength from glass, evenafter kept in high temperature and high humidity conditions of 85° C.and 85% humidity for 1000 hours, the solar cell modules of examplesshowed no change in appearance and the filler layers for a solar cellmodule were not easily separated and were found in good condition.Further, the solar cell modules of examples were found excellent in theelectromotive force decrease ratio. On the other hand, the filler layerfor a solar cell module of Comparative Example 1 did not adhere to glasssince no silane-modified resin was used and could not evaluate for theelectromotive force decrease ratio. The filler layer for a solar cellmodule of Comparative Example 2 was observed turning yellowish afterkept in high temperature and high humidity conditions of 85° C. and 85%humidity for 1000 hours since no master batch was used.

1. A filler layer for a solar cell module containing a silane-modifiedresin obtained by polymerizing an ethylenic unsaturated silane compoundand a polyethylene for polymerization, wherein the filler layer for asolar cell module has a gel fraction of 30% or lower after production ofa solar cell module when the filler layer is used in the solar cellmodule, and further wherein practically no silanol condensation catalystis contained in the filler layer.
 2. The filler layer for a solar cellmodule according to claim 1, further containing a polyethylene foraddition.
 3. The filler layer for a solar cell module according to claim1, wherein the polyethylene for polymerization is at least onepolyethylene selected from a group of a low density polyethylene, amedium density polyethylene, a high density polyethylene, a very lowdensity polyethylene, an ultra low density polyethylene, and a linearlow density polyethylene.
 4. The filler layer for a solar cell moduleaccording to claim 2, wherein the polyethylene for polymerization andthe polyethylene for addition are at least one polyethylene selectedfrom a group of a low density polyethylene, a medium densitypolyethylene, a high density polyethylene, a very low densitypolyethylene, an ultra low density polyethylene, and a linear lowdensity polyethylene.
 5. The filler layer for a solar cell moduleaccording to claim 1, wherein an amount of the silane-modified resincontained therein is in a range of 1 to 80% by weight.
 6. The fillerlayer for a solar cell module according to claim 2, wherein an amount ofthe silane-modified resin contained therein is in a range of 1 to 80% byweight.
 7. The filler layer for a solar cell module according to claim1, wherein Si (silicon) is contained in a form of a polymerized Si atthe amount of 8 ppm to 3500 ppm.
 8. The filler layer for a solar cellmodule according to claim 2, wherein Si (silicon) is contained in a formof a polymerized Si at the amount of 8 ppm to 3500 ppm.
 9. The fillerlayer for a solar cell module according to claim 1, wherein an amount ofthe silanol condensation catalyst contained is 0.05 parts by weight orless in the resin composing the filler layer for a solar cell module of100 parts by weight.
 10. The filler layer for a solar cell moduleaccording to claim 2, wherein an amount of the silanol condensationcatalyst contained is 0.05 parts by weight or less in the resincomposing the filler layer for a solar cell module of 100 parts byweight.
 11. A solar cell module comprising the filler layer for a solarcell module according to claim 1.